Today most if not all surnames are inherited from parents. In the past (as explained elsewhere) surnames had other derivations, ie from places or occupations and a common surname was no guarantee of a similar origin. One route to discover the origin of particular families is to use the science of genetics and molecular biology to study and compare DNA composition in different individuals and derive origin from connections in composition.
Tyrone Bowes, a biotechnologist from Dublin has been researching DNA from a surname perspective for a number of years. As an irishman his studies have included irish surnames and he has created a map of each "clan" name showing the geographical location and spread based on genetic comparisons in DNA of individuals with the same surname. Details are available on his website "Irish OriGenes".
The good news for this website and its family is that Kilkie (and Kilkey which he says is the same) is one of the clans he has investigated. the map below shows his findings.
This information matches the family history evidence that "so far at least" all Kilkie individuals can be traced back to Derry.